/*
 * Copyright (C) 2012 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;

import java.util.Iterator;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * An iterator that transforms a backing iterator; for internal use. This avoids the object overhead
 * of constructing a {@link com.google.common.base.Function Function} for internal methods.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
abstract class TransformedIterator<F extends @Nullable Object, T extends @Nullable Object>
        implements Iterator<T>
{
    final Iterator<? extends F> backingIterator;

    TransformedIterator(Iterator<? extends F> backingIterator)
    {
        this.backingIterator = checkNotNull(backingIterator);
    }

    @ParametricNullness
    abstract T transform(@ParametricNullness F from);

    @Override
    public final boolean hasNext()
    {
        return backingIterator.hasNext();
    }

    @Override
    @ParametricNullness
    public final T next()
    {
        return transform(backingIterator.next());
    }

    @Override
    public final void remove()
    {
        backingIterator.remove();
    }
}
